YOLOv5 Apple Metal Performance Shader (MPS) support (#7878)

* Apple Metal Performance Shader (MPS) device support

Following https://pytorch.org/blog/introducing-accelerated-pytorch-training-on-mac/

Should work with Apple M1 devices with PyTorch nightly installed with command `--device mps`. Usage examples:
```bash
python train.py --device mps
python detect.py --device mps
python val.py --device mps
```

* Update device strategy to fix MPS issue

models/common.py

@@ -331,7 +331,7 @@ class DetectMultiBackend(nn.Module):
                 names = yaml.safe_load(f)['names']
 
         if pt:  # PyTorch
-            model = attempt_load(weights if isinstance(weights, list) else w, map_location=device)
+            model = attempt_load(weights if isinstance(weights, list) else w, device=device)
             stride = max(int(model.stride.max()), 32)  # model stride
             names = model.module.names if hasattr(model, 'module') else model.names  # get class names
             model.half() if fp16 else model.float()